研究者詳細 - 寺田　智樹

論文 - 寺田　智樹

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Landscape-Based View on the Stepping Movement of Myosin VI 招待有り査読有り国際共著

Terada, TP; Nie, QM; Sasai, M

JOURNAL OF PHYSICAL CHEMISTRY B 126 巻 ( 38 ) 頁： 7262 - 7270 2022年9月

Folding pathway of a multidomain protein depends on its topology of domain connectivity 査読有り

Takashi Inanami, Tomoki P. Terada, Masaki Sasai

Proceedings of the National Academy of Sciences of the United States of America 111 巻 ( 45 ) 頁： 15969 - 15974 2014年9月

Coupling of Lever Arm Swing and Biased Brownian Motion in Actomyosin 査読有り国際共著

Qing-Miao Nie, Akio Togashi, Takeshi N. Sasaki, Mitsunori Takano, Masaki Sasai, Tomoki P. Terada

PLoS Computational Biology 10 巻 ( 4 ) 頁： e1003552, 1-13 2014年4月

Time Scales in Epigenetic Dynamics and Phenotypic Heterogeneity of Embryonic Stem Cells 査読有り

Masaki Sasai, Yudai Kawabata, Koh Makishi, Kazuhito Itoh, Tomoki P. Terada

PLoS Computational Biology 9 巻 ( 12 ) 頁： e1003380,1-17 2013年12月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

A remarkable feature of the self-renewing population of embryonic stem cells (ESCs) is their phenotypic heterogeneity: Nanog and other marker proteins of ESCs show large cell-to-cell variation in their expression level, which should significantly influence the differentiation process of individual cells. The molecular mechanism and biological implication of this heterogeneity, however, still remain elusive. We address this problem by constructing a model of the core gene-network of mouse ESCs. The model takes account of processes of binding/unbinding of transcription factors, formation/dissolution of transcription apparatus, and modification of histone code at each locus of genes in the network. These processes are hierarchically interrelated to each other forming the dynamical feedback loops. By simulating stochastic dynamics of this model, we show that the phenotypic heterogeneity of ESCs can be explained when the chromatin at the Nanog locus undergoes the large scale reorganization in formation/dissolution of transcription apparatus, which should have the timescale similar to the cell cycle period. With this slow transcriptional switching of Nanog, the simulated ESCs fluctuate among multiple transient states, which can trigger the differentiation into the lineage-specific cell states. From the simulated transitions among cell states, the epigenetic landscape underlying transitions is calculated. The slow Nanog switching gives rise to the wide basin of ESC states in the landscape. The bimodal Nanog distribution arising from the kinetic flow running through this ESC basin prevents transdifferentiation and promotes the definite decision of the cell fate. These results show that the distribution of timescales of the regulatory processes is decisively important to characterize the fluctuation of cells and their differentiation process. The analyses through the epigenetic landscape and the kinetic flow on the landscape should provide a guideline to engineer cell differentiation.

DOI： 10.1371/journal.pcbi.1003380

Unidirectional Brownian motion observed in an in silico single molecule experiment of an actomyosin motor 査読有り

Mitsunori Takano, Tomoki P. Terada, Masaki Sasai

Proceedings of the National Academy of Sciences of the United States of America 107 巻 ( 17 ) 頁： 7769 - 7774 2010年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

The actomyosin molecular motor, the motor composed of myosin II and actin filament, is responsible for muscle contraction, converting chemical energy into mechanical work. Although recent single molecule and structural studies have shed new light on the energy-converting mechanism, the physical basis of the molecular-level mechanism remains unclear because of the experimental limitations. To provide a clue to resolve the controversy between the lever-arm mechanism and the Brownian ratchet-like mechanism, we here report an in silico single molecule experiment of an actomyosin motor. When we placed myosin on an actin filament and allowed myosin to move along the filament, we found that myosin exhibits a unidirectional Brownian motion along the filament. This unidirectionality was found to arise from the combination of a nonequilibrium condition realized by coupling to the ATP hydrolysis and a ratchet-like energy landscape inherent in the actin-myosin interaction along the filament, indicating that a Brownian ratchet-like mechanism contributes substantially to the energy conversion of this molecular motor.

DOI： 10.1073/pnas.0911830107

Correlation between evolutionary structural development and protein folding 査読有り

Chioko Nagao, Tomoki P. Terada, Tetsuya Yomo, Masaki Sasai

Proceedings of the National Academy of Sciences of the United States of America 102 巻 ( 52 ) 頁： 18950 - 18955 2005年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

Evolution should have played important roles in determining folding mechanisms and structures of proteins. In this article we discuss how the folding mechanisms had been affected by the early stage of evolution through which the uniqueness of structure had developed. Although the process of such early-time evolution has remained a mystery, a plausible scenario is that the evolution of proteins toward the ordered structures was guided by functional selection pressure as demonstrated in vitro and in silico. We examine the in silico functional selection of sequences and show that there is a significant correlation between two different processes toward the unique 3D structure, the evolutionary development of structure through sequence selection, and the folding process of the resultant sequence. This finding could be rephrased as protein folding recapitulates the emergence of topology in the molecular evolution. The correlation suggests a guideline for engineering foldable proteins.

DOI： 10.1073/pnas.0509163102

Conformational change of actomyosin complex drives the multiple stepping movement 査読有り

Tomoki P. Terada, Masaki Sasai, Tetsuya Yomo

Proceedings of the National Academy of Sciences of the United States of America 99 巻 ( 14 ) 頁： 9202-9206 2002年6月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Actin-myosin (actomyosin) generates mechanical force by consuming ATP molecules. We apply the energy landscape perspective to address a controversial issue as to whether the myosin head moves with multiple steps after a single ATP hydrolysis or only a single mechanical event of the lever-arm swinging follows a single ATP hydrolysis. Here we propose a theoretical model in which the refolding of the partially unfolded actomyosin complex and the movement of the myosin head along the actin filament are coupled. A single ATP hydrolysis is followed by the formation of a high free-energy partially unfolded actomyosin complex, which then gradually refolds with a concomitant multiple stepping movement on the way to the lowest free-energy rigor state. The model quantitatively explains the single-molecular observation of the multiple stepping movement and is consistent with structural observations of the disorder in the actomyosin-binding process. The model also explains the observed variety in dwell time before each step, which is not accounted for by previous models, such as the lever-arm or ratchet models.

DOI： 10.1073/pnas.132711799

A Landscape-Based View on the Stepping Movement of Myosin VI 国際共著

Tomoki P. Terada, Qing-Miao Nie, Masaki Sasai

Biophysical Journal 118 巻 ( 3 ) 頁： 436A - 437A 2020年2月

A landscape-based view on the stepping movement of myosin VI 国際共著

T. P. Terada, Q. M. Nie, M. Sasai

European Biophysics Journal with Biophysics Letters 48 巻 ( Supplement 1 ) 頁： S234 - S234 2019年7月

Single-molecular and ensemble-level oscillations of cyanobacterial circadian clock 査読有り

Sumita Das, Tomoki P. Terada, Masaki Sasai

Biophysics and Physicobiology 15 巻頁： 136 - 150 2018年5月

Role of ATP Hydrolysis in Cyanobacterial Circadian Oscillator 査読有り

Sumita Das, Tomoki P. Terada, Masaki Sasai

Scientific Reports 7 巻頁： 17469 2017年12月

Cooperativity and modularity in protein folding 招待有り査読有り

Masaki Sasai, George Chikenji, Tomoki P. Terada

Biophysics and Physicobiology 13 巻頁： 281 - 293 2016年11月

Importance of consensus region of multiple-ligand templates in a virtual screening method 査読有り

Tatsuya Okuno, Koya Kato, Shintaro Minami, Tomoki P. Terada, Masaki Sasai, George Chikenji

Biophysics and Physicobiology 13 巻頁： 149 - 156 2016年7月

真核細胞のルースな遺伝子制御とクロマチン動態招待有り査読有り

笹井理生, 寺田智樹

生物物理 56 巻 ( 2 ) 頁： 106 - 108 2016年3月

ランドスケープ描像で見る細胞分化の物理招待有り査読有り

寺田智樹

日本物理学会誌 70 巻 ( 10 ) 頁： 765 - 769 2015年10月

VS-APPLE: A Virtual Screening Algorithm Using Promiscuous Protein–Ligand Complexes 査読有り

55 巻 ( 6 ) 頁： 1108 - 1119 2015年6月

アクトミオシンの粗視化モデル解析：モーター機能におけるループの柔らかさの重要性招待有り査読有り

寺田智樹

生物物理 55 巻 ( 3 ) 頁： 148 - 150 2015年5月

Conformational flexibility of loops of myosin enhances the global bias in the actin-myosin interaction landscape 招待有り査読有り

Qing-Miao Nie, Masaki Sasai, Tomoki P. Terada

Physical Chemistry Chemical Physics 16 巻 ( 14 ) 頁： 6441-6447 2014年1月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

A long-standing controversy on the mechanism of an actomyosin motor is the role of the Brownian motion of the myosin head in force generation. In order to shed light on this problem, we calculate free-energy landscapes of interaction between an actin filament and the head (S1) of myosin II by using a coarse-grained model of actomyosin. The results show that the free-energy landscape has a global gradient toward the strong-binding site on actin filament, which explains the biased Brownian motion of myosin S1 observed in a single-molecule experiment [Kitamura et al., Nature, 1999, 397, 129 and Biophysics, 2005, 1, 1]. The distinct global gradient in the landscape is brought about only when the conformation of loop 2 at the actin interface of myosin S1 is flexible. The conformational flexibility of loop 3 also contributes to the gradient in the landscape by compensating the role of loop 2. Though the structure of loop 2 is expanded in the weak-binding state, loop 2 shows the larger fluctuation of compaction and expansion due to the actin-myosin interactions as myosin S1 moves toward the strong-binding site on actin filament. Hence, the increase in the compaction-expansion fluctuation of loop 2, the stronger binding of myosin to actin, and the biased Brownian motion of myosin S1 are coupled with each other and should take place in a concurrent way. This predicted coupling should provide opportunities to further test the hypothesis of the biased Brownian motion in actomyosin.

DOI： 10.1039/C3CP54464H

Entropic Mechanism of Allosteric Communication in Conformational Transitions of Dihydrofolate Reductase. 招待有り査読有り

Tomoki P. Terada, Toru Kimura, Masaki Sasai

The Journal of Physical Chemistry B 117 巻 ( 42 ) 頁： 12864 - 12877 2013年5月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The mechanism of allosteric conformational transitions of Escherichia coli dihydrofolate reductase (DHFR) is investigated theoretically by applying a newly developed coarse-grained model. Functional forms of interaction potentials in the model depend on the local structural environments around those interactions to represent the many-residue effects due to atomic packing in each local region, and hence, this model is called "the chameleon model". The chameleon model consistently describes the free-energy landscape of two conformational transitions in the catalytic cycle of DHFR, which we call conformational transition 1 (CT1) and conformational transition 2 (CT2); CT1 is accompanied by the hydride transfer reaction, and CT2 is accompanied by the product ligand release. The transition state of CT1 is entropically stabilized by the disordering of loops at the peripheral regions of the protein, which enhances the positively correlated fluctuations at the center part of the protein, showing that the allosteric communication between distant regions through the central region is intrinsically associated with the entropic stabilization of the transition state. The transition state of CT2 is entropically stabilized through the mechanism that enhances the breathing motion of two domains, showing that the difference in the distribution of interactions brings about the difference in the transition mechanism between CT1 and CT2. The chameleon model opens a way to consistently describe the dynamical energy landscape of enzymatic reactions.

DOI： 10.1021/jp402071m

Dynamical Modeling of Three-Dimensional Genome Organization in Interphase Budding Yeast 査読有り

Naoko Tokuda, Tomoki P. Terada, Masaki Sasai

Biophysical Journal 102 巻 ( 2 ) 頁： 296 - 304 2012年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

Eukaryotic genome is organized in a set of chromosomes each of which consists of a chain of DNA and associated proteins. Processes involving DNA such as transcription, duplication, and repair, therefore, should be intrinsically related to the three-dimensional organization of the genome. In this article, we develop a computational model of the three-dimensional organization of the haploid genome of interphase budding yeast by regarding chromosomes as chains moving under the constraints of nuclear structure and chromatin-chromatin interactions. The simulated genome structure largely fluctuates with the diffusive movement of chromosomes. This fluctuation, however, is not completely random, as parts of chromosomes distribute in characteristic ways to form "territories" in the nucleus. By suitably taking account of constraints arising from the data of the chromosome-conformation-capture measurement, the model explains the observed fluorescence data of chromosome distributions and motions.

DOI： 10.1016/j.bpj.2011.12.005

Synchronization of Circadian Oscillation of Phosphorylation Level of KaiC in vitro 査読有り

Tetsuro Nagai, Tomoki P. Terada, Masaki Sasai

Biophysical Journal 98 巻 ( 11 ) 頁： 2469 - 2477 2010年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

In recent experimental reports, robust circadian oscillation of the phosphorylation level of KaiC has been reconstituted by incubating three cyanobacterial proteins, KaiA, KaiB, and KaiC, with ATP in vitro. This reconstitution indicates that protein-protein interactions and the associated ATP hydrolysis suffice to generate the oscillation, and suggests that the rhythm arising from this protein-based system is the circadian clock pacemaker in cyanobacteria. The mechanism of this reconstituted oscillation, however, remains elusive. In this study, we extend our previous model of oscillation by explicitly taking two phosphorylation sites of KaiC into account and we apply the extended model to the problem of synchrony of two oscillatory samples mixed at different phases. The agreement between the simulated and observed data suggests that the combined mechanism of the allosteric transition of KaiC hexamers and the monomer shuffling between them plays a key role in synchronization among KaiC hexamers and hence underlies the population-level oscillation of the ensemble of Kai proteins. The predicted synchronization patterns in mixtures of unequal amounts of two samples provide further opportunities to experimentally check the validity of the proposed mechanism. This mechanism of synchronization should be important in vivo for the persistent oscillation when Kai proteins are synthesized at random timing in cyanobacterial cells.

DOI： 10.1016/j.bpj.2010.02.036

Mechanism of Robust Circadian Oscillation of KaiC Phosphorylation In Vitro 査読有り

Kohei Eguchi, Mitsumasa Yoda, Tomoki P. Terada and Masaki Sasai

Biophysical Journal 95 巻 ( 4 ) 頁： 1773 - 1784 2008年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

By incubating the mixture of three cyanobacterial proteins, KaiA, KaiB, and KaiC, with ATP in vitro, T. Kondo and his colleagues in recent work reconstituted the robust circadian rhythm of the phosphorylation level of KaiC. This finding indicates that protein-protein interactions and the associated hydrolysis of ATP suffice to generate the circadian rhythm. Several theoretical models have been proposed to explain the rhythm generated in this "protein-only" system, but the clear criterion to discern different possible mechanisms was not known. In this article, we discuss a model based on two basic assumptions: the assumption of the allosteric transition of a KaiC hexamer and the assumption of the monomer exchange between KaiC hexamers. The model shows a stable rhythmic oscillation of the phosphorylation level of KaiC, which is robust against changes in concentration of Kai proteins. We show that this robustness gives a clue to distinguish different possible mechanisms. We also discuss the robustness of oscillation against the change in the system size. Behaviors of the system with the cellular or subcellular size should shed light on the role of the protein-protein interactions in in vivo circadian oscillation.

DOI： 10.1529/biophysj.107.127555

Monomer-Shuffling and Allosteric Transition in KaiC Circadian Oscillation 査読有り

Mitsumasa Yoda, Kohei Eguchi, Tomoki P. Terada, Masaki Sasai

PLoS ONE 2 巻 ( 5 ) 頁： e408,1-8 2007年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

Circadian rhythms in living organisms have long been attributed solely to a transcription-translation loop comprising a negative or positive feedback. The rhythms in cyanobacteria are known to be modulated by kaiC, kaiA and kaiB genes. It was recently shown, however, that their product proteins KaiC, KaiA and KaiB are sufficient to reconstitute the circadian rhythm in the phosphorylation level of KaiC in vitro. It has since been unclear why such an oscillatory behavior can occur in the absence of the apparent transcription-translation feedback. In the meantime, it has been reported that the monomer exchange between KaiC hexamers occurs in a phosphorylation-dependent manner, which suggests that the monomer shuffling is also involved in the circadian rhythm (H. Kageyama et al., Mol. Cell, 23, 161 (2006)). To further clarify the role of the monomer shuffling, we have performed a computational modeling of interactions among Kai proteins assuming the allosteric transition of KaiC hexamer as well as the monomer shuffling. The results show that the existence of both monomer shuffling and allosteric transition can synchronize the phosphorylation level of the KaiC hexamers, and stabilizes its oscillation.

DOI： 10.1371/journal.pone.0000408

タンパク質のダイナミクスとインフォマティクス招待有り査読有り

笹井理生, 寺田智樹

高分子 51 巻 ( 6 ) 頁： 448 2002年6月

分子進化とフォールディング機構招待有り

笹井理生, 寺田智樹

蛋白質核酸酵素 47 巻 ( 6 ) 頁： 677 - 683 2002年5月

Nucleotide binding to the chaperonin GroEL: noncooperative binding of ATP analogs and ADP, and cooperative effect of ATP 査読有り

Tomonao Inobe, Tadashi Makio, Etsuko Takasu-Ishikawa, Tomoki P. Terada, Kunihiro Kuwajima

Biochimica et Biophysica Acta 1545 巻 ( 1-2 ) 頁： 160 - 173 2001年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

Chaperonin-assisted protein folding proceeds through cycles of ATP binding and hydrolysis by GroEL, which undergoes a large structural change by the ATP binding or hydrolysis. One of the main concerns of GroEL is the mechanism of the productive and cooperative structural change of GroEL induced by the nucleotide. We studied the cooperative nature of GroEL by nucleotide titration using isothermal titration calorimetry and fluorescence spectroscopy. Our results indicated that the binding of ADP and ATP analogs to a single ring mutant (SR1), as well as that to GroEL, was non-cooperative. Only ATP induces an apparently cooperative conformational change in both proteins. Furthermore, the fluorescence changes of pyrene-labeled GroEL indicated that GroEL has two kinds of nucleotide binding sites. The fluorescence titration result fits well with a model in which two kinds of binding sites are both non-cooperative and independent of each other. These results suggest that the binding and hydrolysis of ATP may be necessary for the cooperative transition of GroEL.

DOI： 10.1016/S0167-4838(00)00274-0

Equilibrium and Kinetic Studies on Folding of the Authentic and Recombinant Forms of Human α-Lactalbumin by Circular Dichroism Spectroscopy 査読有り国際共著

Tapan K. Chaudhuri, Munehito Arai, Tomoki P. Terada, Teikichi Ikura, Kunihiro Kuwajima

Biochemistry 39 巻 ( 50 ) 頁： 15643 - 15651 2000年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

The equilibrium and kinetics of the unfolding and refolding of authentic and recombinant human α-lactalbumin, the latter of which had an extra methionine residue at the N-terminus, were studied by circular dichroism spectroscopy, and the results were compared with the results for bovine and goat α-lactalbumins obtained in our previous studies. As observed in the bovine and goat proteins, the presence of the extra methionine residue in the recombinant protein remarkably destabilized the native state, and the destabilization was entirely ascribed to an increase in the rate of unfolding. The thermodynamic stability of the native state against the unfolded state was lower, and the thermodynamic stability of the molten globule state against the unfolded state was higher for the human protein than for the other α-lactalbumins previously studied. Thus, the population of the molten globule intermediate was higher during the equilibrium unfolding of human α-lactalbumin by guanidine hydrochloride. Unlike the molten globule states of the bovine and goat proteins, the human α-lactalbumin molten globule showed remarkably more intense circular dichroism ellipticity than the native state in the far-ultraviolet region below 225 nm. During refolding from the unfolded state, human α-lactalbumin thus exhibited overshoot kinetics, in which the alpha-helical peptide ellipticity exceeded the native value when the molten globule folding intermediate was formed in the burst phase. The subsequent folding involved reorganization of nonnative secondary structures. It should be noted that the rate constant of the major refolding phase was approximately the same among the three types of α-lactalbumin and that the rate constant of unfolding was accelerated 18-600 times in the human protein, and these results interpreted the lower thermodynamic stability of this protein.

DOI： 10.1021/bi001735j

Thermodynamics of nucleotide binding to the chaperonin GroEL studied by isothermal titration calorimetry: evidence for noncooperative nucleotide binding 査読有り

Tomoki P. Terada, Kunihiro Kuwajima

Biochimica et Biophysica Acta 1431 巻 ( 2 ) 頁： 269 - 281 1999年5月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

We characterized the thermodynamics of binding reactions of nucleotides ADP and ATPγS (a nonhydrolyzable analog of ATP) to GroEL in a temperature range of 5°C to 35°C by isothermal titration calorimetry. Analysis with a noncooperative binding model has shown that the bindings of nucleotides are driven enthalpically with binding constants of 7×103 M-1 and 4×104 M-1 for ADP and ATPγS, respectively, at 26°C and that the heat capacity change ΔCp is about 100 cal/molcharacterK for both the nucleotides. The stoichiometries of binding were about 8 and 9 molecules for ADP and ATPγS, respectively, per GroEL tetradecamer at 5°C, and both increased with temperature to reach about 14 (ADP) and 12 (ATPγS) for both nucleotides at 35°C. The absence of initial increase of binding heat as well as Hill coefficient less than 1.2, which were obtained from the fitting to the model curve by assuming positive cooperativity, showed that there was virtually no positive cooperativity in the nucleotide bindings. Incorporating a difference in affinity for the nucleotide (ADP and ATPγS) between the two rings of GroEL into the noncooperative binding model improved the goodness of fitting and the difference in the affinity increased with decreasing temperature.

DOI： 10.1016/S0167-4838(99)00049-7

Effect of the Extra N-terminal Methionine Residue on the Stability and Folding of Recombinant α-Lactalbumin Expressed in Escherichia coli 査読有り国際共著

Tapan K. Chaudhuri, Katsunori Horii, Takao Yoda, Munehito Arai, Shinji Nagata, Tomoki P. Terada, Hidefumi Uchiyama, Teikichi Ikura, Kouhei Tsumoto, Hiroshi Kataoka, Masaaki Matsushima, Kunihiro Kuwajima, Izumi Kumagai

Journal of Molecular Biology 285 巻 ( 3 ) 頁： 1179 - 1194 1999年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

The structure, stability, and unfolding-refolding kinetics of Escherichia coli-expressed recombinant goat α-lactalbumin were studied by circular dichroism spectroscopy, X-ray crystallography, and stopped-flow measurements, and the results were compared with those of the authentic protein prepared from goat milk. The electric properties of the two proteins were also studied by gel electrophoresis and ion-exchange chromatography. Although the overall structures of the authentic and recombinant proteins are the same, the extra methionine residue at the N terminus of the recombinant protein remarkably affects the native-state stability and the electric properties. The native state of the recombinant protein was 3.5 kcal/mol less stable than the authentic protein, and the recombinant protein was more negatively charged than the authentic one. The recombinant protein unfolded 5.7 times faster than the authentic one, although there were no significant differences in the refolding rates of the two proteins. The destabilization of the recombinant protein can be fully interpreted in terms of the increased unfolding rate of the protein, indicating that the N-terminal region remains unorganized in the transition state of refolding, and hence is not involved in the folding initiation site of the protein. A comparison of the X-ray structures of recombinant α-lactalbumin determined here with that of the authentic protein shows that the structural differences between the proteins are confined to the N-terminal region. Theoretical considerations for the differences in the conformational and solvation free energies between the proteins show that the destabilization of the recombinant protein is primarily due to excess conformational entropy of the N-terminal methionine residue in the unfolded state, and also due to less exposure of hydrophobic surface on unfolding. The results suggest that when the N-terminal region of a protein has a rigid structure, expression of the protein by E. coli, which adds the extra methionine residue, destabilizes the native state through a conformational entropy effect. It also shows that differences in the electrostatic interactions of the N-terminal amino group with the side-chain atoms of Thr38, Asp37, and Asp83 bring about a difference in the pKa value of the N-terminal amino group between the proteins, resulting in a greater negative net charge of the recombinant protein at neutral pH.

DOI： 10.1006/jmbi.1998.2362

Observation of kaonic hydrogen atom x rays 査読有り国際共著

T.M. Ito, R.S. Hayano, S.N. Nakamura, T.P. Terada, M. Iwasaki, D.R. Gill, L. Lee, A. Olin, M. Salomon, S. Yen, K. Bartlett, G.A. Beer, G. Mason, G. Trayling, H. Outa, T. Taniguchi, Y. Yamashita, R. Seki

Physical Review C 58 巻 ( 4 ) 頁： 2366 - 2382 1998年10月

A new approach to measure kaonic hydrogen X-rays 査読有り国際共著

S.N. Nakamura, M. Iwasaki, K. Bartlett, G.A. Beer, D.R. Gill, R.S. Hayano, T.M. Ito, M. Kuwata, L. Lee, G. Mason, H. Ohkubo, A. Olin, H. Outa, M. Salomon, R. Seki, K. Shibuya, T. Taniguchi, T.P. Terada, G. Trayling, T. Watanabe, Y. Yamashita, S. Yen

Nuclear Instruments and Methods in Physics Research A 408 巻 ( 2-3 ) 頁： 438 - 452 1998年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

Previous kaonic hydrogen X-ray experiments suffered from a poor signal-to-background level. This has been overcome in the present measurement through the use of a gaseous hydrogen target and the imposition of a two-charged-pion tagging requirement. In this paper a full technical description is given of the experimental methods employed.

DOI： 10.1016/S0168-9002(98)00201-0

Observation of Kaonic Hydrogen Kα X Rays 査読有り国際共著

M. Iwasaki, R.S. Hayano, T.M. Ito, S.N. Nakamura, T.P. Terada, D.R. Gill, L. Lee, A. Olin, M. Salomon, S. Yen, K. Bartlett, G.A. Beer, G. Mason, G. Trayling, H. Outa, T. Taniguchi, Y. Yamashita, R. Seki

Physical Review Letters 78 巻 ( 16 ) 頁： 3067 - 3069 1997年4月

Cascade calculation of hadronic hydrogen atoms 査読有り

T.P. Terada and R.S. Hayano

Physical Review C 55 巻 ( 1 ) 頁： 73 - 87 1997年1月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Cascade calculations of hadronic hydrogen atoms are performed to obtain the x-ray yields as a function of the target density. An extension of Leon-Bethe's Stark mixing rates to m(not equal)0 states is made without the introduction of the parameter kSTK, which is necessary in the Borie-Leon model to enhance the Stark mixing rates. Although the energies of their L x rays are too low to observe, we can roughly estimate the 2p absorption width of pionic and kaonic hydrogen atoms from the measured K x-ray yields.

DOI： 10.1103/PhysRevC.55.73

A Pulse-Processor Based on Rise Time Measurement of Trapezoidal Waveforms by Using a Count-Up ADC 査読有り

M. Kuwata, H. Maeda, K. Husimi, S. Ohkawa, M. Iwasaki, S.N. Nakamura, T.M. Ito, T. Terada

IEEE Transactions on Nuclear Science 43 巻 ( 3 ) 頁： 1626 - 1628 1996年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

In order to raise the throughput of low-energy X-ray signals appearing in a background of high-energy pulses, a new pulse-processor that measures the rise time of a trapezoidal waveform instead of the peak height has been developed. A rectangular pre-filter and a gated integrator are used to make the wave-shape at the shaper output linear. A rectangular pulse is formed by adding a differentiated step signal and its integration. The rise time of the trapezoidal waveform is inversely proportional to the height of the input step pulse. Therefore, processing time for a high-energy pulse is shorter than that for low-energy one. Consequently, the pile-up loss of the low-energy X-rays is reduced.

DOI： 10.1109/23.507160

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